12: Acid-base Equilibria

Question 1

Standard enthalpy change of neutralisation definition?

Answer 1

the enthalpy change when solutions of an acid and an alkali react to produce 1 mole of water, under standard conditions

Question 2

Are enthalpy changes always negative or positive?

Answer 2

Negative
Neutralisation reactions are always exothermic

Question 3

Why do enthalpy changes of neutralisation for weak acids vary?

Answer 3

Includes enthalpy to do with the reaction between H+ and OH- as well as enthalpy to do with dissociation

Question 4

How to find the pKa from a titration curve?

Answer 4

pH at half-equivalence point

Question 5

Buffer definition

Answer 5

a solution that minimises changes in pH when small amounts of acid or base are added

Question 6

2 ways of making an acidic buffer?

Answer 6

weak acid + salt of its conjugate base
excess of weak acid + strong base

Question 7

How to make an alkaline buffer?

Answer 7

Weak base + one of its salts

Question 8

Example of an alkaline buffer?
Equilibrium set up?

Answer 8

Ammonia solution + Ammonium chloride
NH4+ <—-> NH3 + H+

Question 9

What pH is blood?

Answer 9

7.4

Question 10

What buffer system is present in blood?
Equilibrium set up?

Answer 10

Carbonic acid - hydrogencarbonate buffer system
H2CO3 <—-> H+ + HCO3-

Question 11

How is the level of H2CO3 in blood controlled?

Answer 11

H2CO3 —> H2O +CO2
Respiration - CO2 breathed out

Question 12

How is the level of HCO3- controlled in blood?

Answer 12

Kidneys - excreted in urine